The present invention relates generally to composite tubular structural members having attachment means at their ends. In particular, this invention relates to such a composite tubular structure in which the end of the tube is precisely formed in a flared or tapered configuration to close dimensional tolerances. A method for fabricating such a tube is thoroughly described in U.S. Pat. No. 4,849,152 describing a cone control method for fabricating composite tubes. In this referenced patent, a composite tube is formed by means of winding preimpregnated composite materials on a mandrel having a desired shape and the dimensions desired for the finished tube. In particular, this referenced patent describes a means of forming a precision flared or tapered end on such a tube for means of adapting it to a coupling system.
This invention describes such a composite tubular strut and in particular the means of attaching to the ends of the tubing an end structure for allowing attachment of the strut into the next assembly. As will be described, the strut may be manufactured to a precise length strut with its end fitting without requiring incorporation of metallic ends in the tube or drilling or otherwise cutting the fibers of the tube in assembly. Additionally, the end fittings may be removed and replaced without damaging the tube.
In the prior art of composite tubular assemblies, attachment of the end assemblies has required that means for such attachment being incorporated in the tube. For example, an end attachment ring may be wound into the end of the tube when the tube is fabricated and cured. In these assemblies, the difficulty is in assuring secure attachment of the metal fitting to the composite tube. The failure of such assemblies is usually caused by the composite member separating from the metallic end piece. To prevent such failure, it is common practice to drill matching holes through the tube and its end piece and secure them together using rivets, threaded members or other conventional fastening means. This method assures the integrity of the metal to composite attachment, however, drilling holes through a composite tube cuts the fibers drilled and causes a weakness in the tube possibly reducing its useful life. In addition, the presence of holes and fasteners in the metal fitting subject it to fretting fatigue failures. Additionally, these methods of applying an end piece to a tube do not allow the end piece to be replaced or changed to an alternate method of attachment.
It would be desirable to have a composite tubular strut with an attachment fitting in which the fittings may be changed or the tube changed without damage to any of the other parts. It is also desirable to provide an end attachment to a composite tube without cutting or drilling the tube fibers to make such an attachment.